Brexit to Complicate Trans-Atlantic Cooperation

Obama seeks to minimize impact on U.S. of the U.K. leaving the European Union

WASHINGTON—The U.K.’s decision to leave the European Union dramatically expands the portfolio of foreign-policy challenges the next U.S. president will inherit, complicating critical decisions to address instability across the globe.

President Barack Obama is unexpectedly embarking on a high-stakes effort during his last months in office to work out what a senior administration official called “alternative pathways” for Europe, an effort that accelerates during a trip to Poland next week.